Eli had too many fish in his old fish tank. He got a new fish tank and moved $18$ fish from the old tank to the new tank. He still had $23$ fish in his old tank. How many fish were in Eli's old fish tank at the start?
To find the ${\text{total}}$ number of fish Eli had to start with, we start with the number of ${\text{Fish in new tank}}$, and add the number of ${\text{Fish left in the old tank}}$. $?$ $18$ $23$ Total fish in old tank Fish in new tank Fish left in the old tank ${18} + {23} = {\Box}$ Let's add to find the total number of fish. $$ $$ $$ ${+}$ $$ $$ $$ ${=}$ $$ $$ $$ $$ $$ ${18} + {23} = {41}$ There were ${41}$ fish in Eli's old tank at the start.